JP2024062966A - Front plate for foldable device and foldable device - Google Patents

Abstract

To provide a front plate for a foldable device having an excellent resistance to impact.SOLUTION: The front plate sequentially includes a resin film, an impact absorption layer, one of a resin film and a super-thin glass, and an impact absorption layer when is seen from a visual side. The storage elastic modulus E' is 2 GPa or less and the thickness of the super-thin glass is 100 μm or less when the measured temperature of the impact absorption layer is 25°C and the frequency is 1.0×106 Hz.SELECTED DRAWING: None

Description

The present invention relates to a front panel for a foldable device and a foldable device.

The displays used in foldable devices are generally made of thin resin materials to enable bending. This means that the surface cannot be covered with protective glass, and shocks from dropping the device or writing with a stylus are transmitted to the inside, affecting the display itself.
An object of the present invention is to provide a front panel for a foldable device, which has excellent impact resistance.

The present inventors have conducted extensive research and found that the above problems can be solved by the following means.
＜1＞
A front panel having, from the viewing side, a resin film, an impact absorbing layer, a resin film or ultra-thin glass, and an impact absorbing layer in that order, wherein the impact absorbing layer has a storage modulus E' of 2 GPa or less at a measurement temperature of 25°C and a frequency of 1.0 x 10 ⁶ Hz, and the ultra-thin glass has a thickness of 100 μm or less.
＜2＞
A foldable device using the front panel described in <1>.

The present invention provides a front panel for a foldable device that can be used in the foldable device and has excellent impact resistance.

Hereinafter, the embodiments of the present invention will be described in detail, but the present invention is not limited to these.
In this specification, when a numerical value represents a physical property value, characteristic value, etc., the expression "(Numerical value 1) to (Numerical value 2)" means "(Numerical value 1) or more and (Numerical value 2) or less."
In this specification, the term "(meth)acrylate" means "at least one of acrylate and methacrylate". The same applies to "(meth)acrylic acid", "(meth)acryloyl", etc. In this specification, each component may use one substance corresponding to each component alone or two or more substances in combination. Here, when two or more substances are used in combination for each component, the content of the component refers to the total content of the substances used in combination, unless otherwise specified. In addition, the bonding direction of the divalent group described in this specification is not particularly limited.

<Ultra-thin glass>
Ultra-thin glass refers to glass having a thickness of 100 μm or less. Although not particularly limited, from the viewpoint of, for example, bendability, the thickness is preferably 50 μm or less, and more preferably 30 μm or less. In addition, the thickness is preferably 5 μm or more, and more preferably 10 μm or more. It is preferable that the glass is chemically strengthened.

The ultra-thin glass surface may have a protective layer. The protective layer is preferably a protective layer including at least one of the following (A) to (C) disclosed in WO2022/209923:
(A) A polymer of a polymerizable compound having one or more hydrogen-bonding groups and three or more (meth)acrylic groups in the molecule, a hydrogen-bonding proton value of 3.5 mol/kg or more, and a (meth)acrylic value of 4.8 mol/kg or more. (B) A compound containing a metal coordinate bond. (C) A compound containing a host-guest bond.

The protective layer may contain a slipping agent. Examples of suitable slipping agents include fluorine-containing compounds such as RS-90 (manufactured by DIC Corporation) and polymerizable resins (silicone-containing compounds) disclosed in JP-A-2015-168719.

<Shock absorbing layer>
The impact absorbing layer has a storage modulus E' of 2 GPa or less at a frequency of 1.0 x 10 ⁶ Hz at a measurement temperature of 25°C. From the viewpoint of impact resistance, it is preferably 1.5 GPa or less, more preferably 1.0 GPa or less, further preferably 0.8 GPa or less, and most preferably 0.5 GPa or less.

The impact absorbing layer preferably has a maximum value of tan δ in the frequency range of 10 ^-1 to 10 ¹⁵ Hz (1.0 x 10 ^-1 to 1.0 x 10 ¹⁵ Hz) at 25 ° C., more preferably has a maximum value in the range of 10 ³ to 10 ¹⁵ Hz (1.0 x 10 ³ to 1.0 x 10 ¹⁵ Hz), even more preferably has a maximum value in the range of 10 ⁵ to 10 ¹⁵ Hz, and particularly preferably has a maximum value in the range of 10 ⁵ to 10 ¹⁰ Hz (1.0 x 10 ⁵ to 1.0 x 1010 Hz) at 25 ° C. In this case, it is sufficient to have at least one maximum value of tan δ in the frequency range of 10 ^-1 to 10 ¹⁵ Hz at 25 ° C., and may have two or more maximum values of tan δ in the frequency range of 10 ^-1 to 10 ¹⁵ Hz. In addition, there may be a further maximum value of tan δ in a frequency range outside the frequency range of 10 ⁻¹ to 10 ¹⁵ Hz, and this maximum value may be the maximum value of tan δ of the impact absorbing layer.

[Measurement of storage modulus by dynamic viscoelasticity measurement and calculation of tan δ]
In the present invention, the storage modulus E' at 25°C and a frequency of 10 ⁶ Hz is determined by a tensile deformation mode using a dynamic viscoelasticity measuring device. Similarly, for the relationship between frequency and tan δ at 25°C of the impact absorbing layer, a frequency-tan δ graph is created by a tensile deformation mode using a dynamic viscoelasticity measuring device, and the maximum value of tan δ and the frequency at which the maximum value is obtained are determined.
Specifically, the method described below is used.

<Sample preparation method>
An impact absorbing material (also referred to as an impact absorbing layer material or an impact absorbing layer constituting material), such as a composition for forming an impact absorbing layer described below, is dissolved or melted in a solvent to prepare a coating liquid. The coating liquid is applied to the release-treated surface of a release-treated PET (polyethylene terephthalate) sheet so that the thickness after drying is 40 μm. After drying, the impact absorbing layer is peeled off from the release PET sheet to prepare a test piece of the impact absorbing layer.
<Measurement method>
Using a dynamic viscoelasticity measuring device (manufactured by IT Measurement & Control Co., Ltd., product name: DVA-225), measurements are performed under the following conditions in the "step heating/frequency dispersion" mode for the above test piece that has been previously conditioned for 2 hours or more at a temperature of 25° C. and a relative humidity of 60%, and then, using "master curve" editing, master curves of tan δ, storage modulus, and loss modulus versus frequency at 25° C. are obtained. From the obtained master curve, the maximum value of tan δ and the frequency showing the maximum value are determined.
Sample: 5 mm x 50 mm
Test mode: Tensile deformation mode Grip distance: 20 mm
Set distortion: 0.10%
Measurement temperature: -100℃ to 40℃
Temperature increase condition: 2° C./min

(Impact absorbing layer constituent material)
The impact absorbing layer constituting material having a storage modulus E' of 1 GPa or less at 25°C and a frequency of 10 ⁶ Hz (1.0 x 10 ⁶ Hz) may be made of a resin or an elastomer (including oil-extended rubber).

The above resins include polystyrene resins, polyamide resins, urethane resins, (meth)acrylate resins (also called (meth)acrylic resins, meaning (meth)acrylic acid ester resins, etc.), and modified resins of these resins. Urethane resins include urethane-modified polyester resins and urethane resins. Of the above resins, (meth)acrylate resins are preferred.

Examples of the elastomer include block (co)polymers of conjugated dienes and hydrogenated products thereof, (meth)acrylic block (co)polymers (meaning, for example, (co)polymers having poly(meth)acrylic acid ester as a block unit), styrene block (co)polymers and hydrogenated products thereof ((co)polymers having a polymer of an aromatic vinyl compound (preferably polystyrene) as a block unit and hydrogenated products thereof, for example, a block copolymer of a polymer of an aromatic vinyl compound and a polymer containing a conjugated diene and a hydrogenated block copolymer of a polymer of an aromatic vinyl compound and a polymer containing a conjugated diene), ethylene-α-olefin block (co)polymers and hydrogenated products thereof (a ... Examples of the elastomer include olefin-based copolymers, polar group-modified olefin-based copolymers, elastomers composed of a polar group-modified olefin-based copolymer and at least one of a metal ion and a metal compound, nitrile-based rubbers such as acrylonitrile-butadiene-based rubber, butyl rubber, acrylic rubber, thermoplastic elastomers such as thermoplastic polyolefin elastomers (TPO), thermoplastic polyurethane elastomers (TPU), thermoplastic polyester elastomers (TPEE), thermoplastic polyamide elastomers (TPAE), and diene-based elastomers (1,2-polybutadiene, etc.), silicone-based elastomers, and fluorine-based elastomers.
However, the block (co)polymer of the conjugated diene does not contain a polystyrene block.
The elastomer is preferably a (meth)acrylic block (co)polymer or a styrene block (co)polymer and a hydrogenated product thereof. Preferred examples of the (meth)acrylic block (co)polymer include a block copolymer of polymethyl methacrylate and poly n-butyl acrylate (also referred to as a "PMMA-PnBA block copolymer"). Preferred examples of the styrene block (co)polymer and a hydrogenated product thereof include a block copolymer of a polymer containing at least one of isoprene and butadiene and polystyrene, and a hydrogenated product thereof. The polymer containing at least one of isoprene and butadiene may contain, for example, butene as a component other than isoprene and butadiene.
Among these, the elastomer is more preferably a hydrogenated product of a (meth)acrylic block (co)polymer or a styrene block (co)polymer, and further preferably a PMMA-PnBA copolymer or a hydrogenated product of a block copolymer of a polymer containing at least one of isoprene and butadiene and polystyrene.

The resin or elastomer that may be contained in the impact absorbing layer may be synthesized by a known method, or a commercially available product may be used, such as Clarity LA1114, Clarity LA2140, Clarity LA2250, Clarity LA2330, Clarity LA4285, Hybra 5127, Hybra 7311F, Septon 2104, and Septon 2063 (all of which are product names manufactured by Kuraray Co., Ltd.).
The impact absorbing layer is preferably made of at least one of the above-mentioned resins and elastomers.

The weight average molecular weight of the resin or elastomer is preferably from 10,000 to 1,000,000, and more preferably from 50,000 to 500,000, from the viewpoint of the balance between solubility in a solvent and the storage modulus.
When the impact absorbing layer is formed, these resins or elastomers (polymers) may be used as the only constituent material.
In addition, as described below, when the impact absorbing layer is formed using various additives in addition to the above resin or elastomer, in consideration of the above storage modulus in the impact absorbing layer, the content of the above resin or elastomer in the solid content constituting the impact absorbing layer is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more. In addition, there is no particular limit to the content of the above resin or elastomer, but for example, it is preferably 99.9% by mass or less, more preferably 95% by mass or less, and even more preferably 90% by mass or less.
In the case of forming the impact absorbing layer using the above-mentioned resin or elastomer together with the polymerizable group-containing compound and the polymerization initiator described below, and in the case of forming the impact absorbing layer using the below-mentioned polymerizable group-containing compound and the polymerization initiator without using the above-mentioned resin or elastomer, the contents of these constituent materials (resin, elastomer, polymerizable group-containing compound, and polymerization initiator) in the total solids content can be the same as those described for the above-mentioned resin or elastomer content.

In addition to the above resin or elastomer, the impact absorbing layer may be formed using a composition containing additives such as softeners, plasticizers, lubricants, crosslinking agents, crosslinking assistants, photosensitizers, antioxidants, antiaging agents, heat stabilizers, flame retardants, antibacterial agents, antifungal agents, weather resistance agents, ultraviolet absorbers, tackifiers, nucleating agents, pigments, dyes, organic fillers, inorganic fillers, silane coupling agents and titanium coupling agents, polymerizable group-containing compounds, polymerization initiators or polymers other than the above resins or elastomers (hereinafter also referred to as other polymers) as a constituent material. That is, the impact absorbing layer may be formed using a resin composition or an elastomer composition.
Hereinafter, the composition used to form the impact absorbing layer will be referred to as an impact absorbing layer forming composition.

The inorganic filler added to the impact absorbing layer is not particularly limited, but for example, silica particles, zirconia particles, alumina particles, mica and talc can be used. These may be used alone or in combination of two or more kinds.
From the viewpoint of dispersibility in the impact absorbing layer, silica particles are preferred.

The surface of the inorganic filler may be treated with a surface modifier having a functional group capable of bonding or adsorbing to the inorganic filler in order to increase the affinity with the resin constituting the impact absorbing layer. Examples of such surface modifiers include metal alkoxide surface modifiers such as silane, aluminum, titanium, and zirconium, as well as surface modifiers having anionic groups such as phosphate groups, sulfate groups, sulfonic acid groups, and carboxylate groups.

Considering the balance between the storage modulus and tan δ in the impact absorbing layer, the content of the inorganic filler is preferably 1 to 40 mass %, more preferably 5 to 30 mass %, and even more preferably 5 to 15 mass % of the solid content constituting the impact absorbing layer. The size (average primary particle size) of the inorganic filler is preferably 10 nm to 100 nm, and more preferably 15 to 60 nm. The average primary particle size of the inorganic filler can be determined from an electron microscope photograph. If the particle size of the inorganic filler is equal to or greater than the above-mentioned preferable lower limit, the effect of improving the storage modulus is obtained, and if it is equal to or less than the above-mentioned preferable upper limit, there is no possibility of causing an increase in haze. The shape of the inorganic filler may be any of plate-like, spherical, and non-spherical.

Specific examples of inorganic fillers include ELECOM V-8802 (manufactured by JGC Catalysts & Chemicals, spherical silica microparticles with an average primary particle size of 12 nm), ELECOM V-8803 (manufactured by JGC Catalysts & Chemicals, irregularly shaped silica microparticles), MIBK-ST (manufactured by Nissan Chemical Industries, Ltd., spherical silica microparticles with an average primary particle size of 10-20 nm), MEK-AC-2140Z (manufactured by Nissan Chemical Industries, Ltd., spherical silica microparticles with an average primary particle size of 10-20 nm), MEK-AC-4130 (manufactured by Nissan Chemical Industries, Ltd., spherical silica microparticles with an average primary particle size of 40-50 nm), MIBK-SD-L (manufactured by Nissan Chemical Industries, Ltd., spherical silica microparticles with an average primary particle size of 40-50 nm), and MEK-AC-5140Z (manufactured by Nissan Chemical Industries, Ltd., spherical silica microparticles with an average primary particle size of 70-100 nm).

The tackifier added to the impact absorbing layer is not particularly limited, but examples thereof include rosin ester resin, hydrogenated rosin ester resin, petrochemical resin, hydrogenated petrochemical resin, terpene resin, terpene phenol resin, aromatic modified terpene resin, hydrogenated terpene resin, and alkylphenol resin. These tackifiers may be used alone or in combination of two or more.

Considering the balance between the storage modulus and tan δ in the impact absorbing layer, the content of the tackifier is preferably 1 to 80 mass % of the solid content constituting the impact absorbing layer, and more preferably 5 to 70 mass %.

Specific examples of tackifiers include Super Ester A75, A115, and A125 (all rosin ester resins manufactured by Arakawa Chemical Industries Co., Ltd.), Petrotack 60, 70, 90, 100, 100V, and 90HM (all petrochemical resins manufactured by Tosoh Corporation), YS Polystar T30, T80, T100, T115, T130, T145, and T160 (terpene phenol resins manufactured by Yasuhara Chemical Co., Ltd.), and YS Resin PX800, PX1000, PX1150, and PX1250 (terpene resins manufactured by Yasuhara Chemical Co., Ltd.).

The softener added to the impact absorbing layer is not particularly limited, but may be at least one of mineral oils such as naphthenic, paraffinic and aromatic, vegetable oils such as castor oil, cottonseed oil, linseed oil, rapeseed oil, soybean oil, palm oil, safflower oil, peanut oil, Japan wax, pine oil and olive oil, and synthetic softeners for various rubbers and resins. The number average molecular weight of the softener is preferably 200 or more, more preferably 300 or more, in order to suppress bleed-out, and is preferably 1000 or less, more preferably 800 or less, in order to suppress stickiness.

Considering the balance between the storage modulus and tan δ in the impact absorbing layer, the content of the softener is preferably 70% by mass or less, and more preferably 10% by mass or more and 50% by mass or less, of the solid content constituting the impact absorbing layer.

Specific examples of softeners include MORESCO White P-40, P-55, P-60, P-70, P-80, P-100, P-120, P-150, P-200, P-260 and P-350P (all paraffin-based oils manufactured by MORESCO), Diana Process Oil NS-24, NS-100, NM-26, NM-30, NM-40, NM-50, NM-60, NM-70, NM-80, NM-90, NM-100, NM-120, NM-140, NM-160, NM-180, NM-200, NM-220, NM-240, NM-260, NM-350P, NM-400, NM-400, NM-500, NM-600, NM-700, NM-800, NM-900, NM-1000, NM-1200, NM-1400, NM-1600, NM-1800, NM-1800, NM-1800, NM-1800, NM-1800, NM-1800, NM-1800, NM-20 ...3000, NM-3000, NM-3000, NM-4000, NM-4000, NM-5000, NM-6000, NM-7000, NM-8000, NM-9000, NM-1 68, NM-150, NM-280, NP-24, NU-80 and NF-90 (all naphthenic oils manufactured by Idemitsu Kosan) and Diana Process Oil AC-12, AC-460, AE-24, AE-50, AE-200, AH-16 and AH-58 (all aromatic oils manufactured by Idemitsu Kosan).

The polymerizable group-containing compound that can be included in the composition for forming the impact absorbing layer, such as the resin composition or elastomer composition used to form the impact absorbing layer, may be any of a polymerizable group-containing polymer, a polymerizable group-containing oligomer, and a polymerizable group-containing monomer, and may be an elastomer (including rubber) having a polymerizable group. Specific examples include commercially available products such as Artcure RA331MB and RA341 (both of which are product names manufactured by Negami Chemical Industries, Ltd.), Kuraplane UC-102M and 203M (both of which are product names manufactured by Kuraray Co., Ltd.), and Selm Elastomer SH3400M (product name manufactured by Advanced Soft Materials Co., Ltd.), as well as the radical polymerizable compounds and cationically polymerizable compounds described below.

When the resin composition or elastomer composition used to form the impact absorbing layer contains a polymerizable group-containing compound, it is preferable that the composition further contains a polymerization initiator. Specific examples of the polymerization initiator include the polymerization initiators described below.
In addition, it is also preferable that the impact absorbing layer is formed using a composition for forming the impact absorbing layer that does not contain the above-mentioned resin or elastomer and has at least a polymerizable group-containing compound and a polymerization initiator. Among them, an impact absorbing layer obtained by curing a composition containing a rubber such as polyisoprene having a radical polymerizable group as a polymerizable group and a polymerization initiator is preferably mentioned.

(Thickness of impact absorbing layer)
From the viewpoint of further improving the impact absorbing property, the thickness of the impact absorbing layer is preferably from 1 μm to 100 μm, more preferably from 5 μm to 80 μm, and even more preferably from 10 μm to 80 μm.

(Method of forming impact absorbing layer)
The method for forming the impact absorbing layer is not particularly limited, and examples thereof include coating method, casting method (solventless casting method and solvent casting method), pressing method, extrusion method, injection molding method, casting method, and inflation method. In detail, the impact absorbing layer is prepared by dissolving or dispersing the impact absorbing layer constituent material in a solvent, or preparing a molten liquid of the components constituting the impact absorbing material (specifically, the resin or elastomer, etc.), and then applying this liquid or molten liquid to a resin film, and then removing the solvent, etc., as necessary, to prepare an impact absorbing layer on a resin film (or a resin film of a resin film with a HC layer).
The solvent is not particularly limited, and for example, the description of the solvent in the curable composition for forming the HC layer can be applied, and preferred examples include methyl isobutyl ketone and toluene.
The mixing ratio of the solvent and the solid content is not particularly limited and can be appropriately adjusted. For example, the ratio of the solid content to the total amount of the solvent and the solid content can be 10 to 90 mass %.

It is also possible to produce an impact absorbing layer on a resin film (or the resin film of a resin film with an HC layer) by applying an impact absorbing layer material to the release treated surface of a release sheet in the same manner as above, drying it, forming a sheet with an impact absorbing layer, and bonding the impact absorbing layer of this sheet to a resin film.

When the impact absorbing layer is made of a resin, the impact absorbing layer may be made of a resin that is not crosslinked, or may be made of a resin that is at least partially crosslinked. There is no particular limitation on the method of crosslinking the resin, and examples of the method include a means selected from electron beam irradiation, ultraviolet irradiation, and a method using a crosslinking agent (e.g., organic peroxide, etc.). When crosslinking the resin is performed by electron beam irradiation, crosslinking can be formed by irradiating the obtained impact absorbing layer before crosslinking with an electron beam using an electron beam irradiation device. In addition, in the case of ultraviolet irradiation, crosslinking can be formed by the effect of a photosensitizer such as a photopolymerization initiator that is blended as necessary by irradiating the obtained impact absorbing layer before crosslinking with ultraviolet rays using an ultraviolet irradiation device. Furthermore, when a crosslinking agent is used, crosslinking can be formed by a crosslinking agent such as an organic peroxide that is blended as necessary, and further a crosslinking assistant, by heating the obtained impact absorbing layer before crosslinking in an atmosphere that does not contain air, such as a nitrogen atmosphere.
When the polymerizable group-containing compound is contained, it is preferable to form the impact absorbing layer by crosslinking using any one of electron beam irradiation, ultraviolet ray irradiation, and a crosslinking agent.

The impact absorbing layer may be made of a pressure sensitive adhesive or a bonding agent.
As the adhesive, for example, a rubber-based adhesive, an acrylic-based adhesive, a silicone-based adhesive, a urethane-based adhesive, a vinyl alkyl ether-based adhesive, a polyvinylpyrrolidone-based adhesive, a polyacrylamide-based adhesive, a cellulose-based adhesive, etc. can be suitably used.

<Resin film>
The material of the resin film used in the present invention is not particularly limited.
Examples of the resin film include acrylic resin films, polycarbonate (PC) resin films, cellulose ester resin films such as triacetyl cellulose (TAC) resin films, polyethylene terephthalate (PET) resin films, polyolefin resin films, polyester resin films, polyimide resin films, polyamide resin films, polyamideimide resin films, and acrylonitrile-butadiene-styrene copolymer resin films.
From the viewpoint of foldability and impact absorption resistance, polyethylene terephthalate (PET) resin films, polyester resin films, polyimide resin films, polyamide resin films, and polyamideimide resin films are particularly suitable.
Furthermore, the resin film may include a hard coat layer and/or an abrasion-resistant layer on either or both sides thereof. When including one side, it is preferable to arrange it on the visible side.

The present invention will be explained in more detail below with reference to examples, but the scope of the present invention should not be construed as being limited thereto.

Example 1
(Resin film 1)
As the resin film 1, a PET film having a thickness of 44 μm (Cosmoshine SRF TA044, manufactured by Toyobo Co., Ltd.) was used.

(Synthesis of compound (A1))
In a 1000-milliliter flask (reaction vessel) equipped with a thermometer, a stirrer, a reflux condenser, and a nitrogen inlet tube, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane (98.6 g, 400 mmol), acetone (100 g), potassium carbonate (553 mg, 4.0 mmol), and pure water (76.0 g, 4000 mmol) were mixed under a nitrogen stream and stirred at 50° C. for 5 hours. After the reaction liquid was returned to room temperature (23° C.), methyl isobutyl ketone (200 g) and 5% by mass saline (200 g) were added, and the organic layer was extracted. The organic layer was washed twice with 5% by mass saline (200 g) and twice with pure water (200 g), and then concentrated under reduced pressure to obtain 131.1 g of compound (A1) as a 61.1% by mass methyl isobutyl ketone (MIBK) solution (yield 93%). The compound (A1) had a number average molecular weight (Mn) of 5,610, a weight average molecular weight (Mw) of 17,400, and a molecular weight dispersity (Mw/Mn) of 3.1.

In the above formula, (SiO _1.5 ) represents a structural portion constituted by a siloxane bond (Si—O—Si) in the polyorganosilsesquioxane, similar to the above-mentioned [SiO _3/2 ].

<Preparation of Cured Layer-Forming Composition>
(Cured layer forming composition HC-1)
CPI-100B (a photocationic polymerization initiator, manufactured by San-Apro Co., Ltd.) and MIBK (methyl isobutyl ketone) were added to the MIBK solution containing the compound (A1), and the contents of the respective components were adjusted as follows, and the mixture was charged into a mixing tank and stirred. The resulting composition was filtered through a polypropylene filter having a pore size of 0.45 μm to obtain a cured layer-forming composition HC-1.

MIBK solution of compound (A1) (solid content concentration: 61.1% by mass)
84.3 parts by mass of an MIBK solution of interlayer adhesion agent (Z) (solid content concentration 19.1% by mass)
5.65 parts by weight CPI-100B (solid content concentration 40% by weight) 3.57 parts by weight MIBK 6.50 parts by weight

The interlayer adhesion agent (Z) is a compound represented by the following structural formula. The content ratio of the repeating units in the following structural formula is a molar ratio.

<Preparation of Composition for Forming Abrasion-Resistant Layer>
(Composition for forming abrasion-resistant layer HC-2)
A-TMMT (manufactured by Shin-Nakamura Kogyo Co., Ltd.), compound (A-1), Irgacure 127 (manufactured by BASF), compound 4 (conductive compound A), and Megafac RS-90 (manufactured by DIC Corporation) were charged into a mixing tank containing MIBK (methyl isobutyl ketone) in advance, and stirred. The content of each component is as shown below. The obtained composition was filtered through a polypropylene filter having a pore size of 0.45 μm to obtain abrasion-resistant layer-forming composition HC-2.

A-TMMT 26.2 parts by weight Compound (A-1) 7.1 parts by weight Irgacure 127 1.0 parts by weight Compound 4 (conductive compound A) 3.2 parts by weight Megafac RS-90 3.5 parts by weight MIBK 50.4 parts by weight

The above compound (A-1) is a compound represented by the following structural formula:

The above compound 4 (conductive compound A) is a compound represented by the following structural formula. The content ratio of the repeating units in the following structural formula is a molar ratio.

<Preparation of hardened layer and abrasion-resistant layer>
The obtained composition for forming a cured layer HC-1 was applied onto a resin film 1 (PET film) with a bar coater, then placed in an oven and thermally dried at 120°C for 1 minute, and then irradiated with ultraviolet light at an irradiation dose of 600 mJ/ ^cm2 to perform a photocuring treatment. The film thickness of the cured layer was 17 μm.
The above-mentioned abrasion-resistant layer-forming composition HC-2 was further applied on the prepared cured layer with a bar coater, dried at 120 ° C. for 1 minute, and then irradiated with ultraviolet light at an irradiation dose of 600 mJ / cm 2 under conditions of 25 ° C., oxygen concentration of 100 ppm, and illuminance of 60 mW / cm 2. Thereafter, an air-cooled mercury lamp was used to irradiate ultraviolet light at an illuminance of 60 mW / cm ² and an irradiation dose of 600 mJ / cm ² under conditions of 100 ° C. and oxygen concentration of 100 ppm to form an abrasion-resistant layer. The film thickness of the obtained abrasion-resistant layer was 1 μm.

<Preparation of Impact Absorbing Layer-Forming Composition>
(Impact absorbing layer forming composition CU-1)
Clarity LA2140 (Kuraray Co., Ltd.) was added to a mixing tank containing MIBK (methyl isobutyl ketone) in advance, and stirred. The content of each component is as shown below. The obtained composition was filtered through a polypropylene filter with a pore size of 10 μm to obtain impact absorbing layer forming composition CU-1.

Clarity LA2140 25.0 parts by weight MIBK 75.0 parts by weight

<Preparation of Impact Absorbing Layer 1>
The composition for forming an impact absorbing layer CU-1 obtained above was applied to the surface opposite to the side having the cured layer of the resin film 1 having the cured layer and the abrasion-resistant layer obtained above, and dried to form an impact absorbing layer 1.
Specifically, the coating and drying methods were as follows: By the die coating method using a slot die described in Example 1 of JP-A-2006-122889, the impact absorbing layer forming composition CU-1 was coated under the condition of a conveying speed of 30 m/min so that the film thickness after drying would be 80 μm, and the film was dried at an atmospheric temperature of 60° C. for 150 seconds to prepare the impact absorbing layer 1.

<Lamination of Resin Film 2>
A PET film (Cosmoshine SRF TA044, manufactured by Toyobo Co., Ltd.) having a thickness of 44 μm was laminated as the resin film 2 to the surface of the impact absorbing layer 1 obtained above opposite to the resin film 1. Specifically, the resin film 2 was pressed onto the impact absorbing layer 1 and pressed with a rubber roller to laminate them.

(Impact absorbing layer 2)
The impact absorbing layer 2 was made of a 20 μm thick adhesive SK-2057 (manufactured by Soken Chemical Industries, Ltd.).

Impact absorbing layer 2 was attached to the surface of resin film 2 attached above, opposite the surface having impact absorbing layer 1. Specifically, one side of the protective film on both sides of adhesive SK-2057 was peeled off, and the exposed adhesive surface was brought into contact with the surface of resin film 2 opposite the surface having impact absorbing layer 1, and the two were pressed together with a rubber roller, after which the protective film on the pressure surface of the rubber roller was peeled off to obtain a front panel.

Example 2
A front panel was prepared in the same manner as in Example 1, except that impact absorbing layer 2 in Example 1 was prepared in the same manner as impact absorbing layer 1 in Example 1.

Example 3
The impact absorbing layer 1 of Example 2 was prepared in the same manner as the impact absorbing layer 2 of Example 1, and the resin film 2 of Example 2 was changed to a chemically strengthened ultra-thin glass (thickness μ30 μm). A front panel was prepared in the same manner as Example 2.

Example 4
A front panel was produced in the same manner as in Example 1, except that the resin film 2 in Example 1 was changed to chemically strengthened ultra-thin glass (thickness μ30 μm).

Example 5
A front panel was produced in the same manner as in Example 2, except that resin film 2 in Example 2 was changed to chemically strengthened ultra-thin glass (thickness μ30 μm).

Example 6
A front panel was produced in the same manner as in Example 5, except that the impact absorbing layer 1 and the impact absorbing layer 2 in Example 5 were produced using the impact absorbing layer-forming composition CU-2 shown below.

(Impact absorbing layer forming composition CU-2)
Hybler 7311F (Kuraray Co., Ltd.) was added to a mixing tank containing MIBK (methyl isobutyl ketone) in advance and stirred. The content of each component is as shown below. The obtained composition was filtered through a polypropylene filter with a pore size of 10 μm to obtain impact absorbing layer forming composition CU-2.

Hybra 7311F 25.0 parts by weight MIBK 75.0 parts by weight

(Example 7)
A front panel was produced in the same manner as in Example 5, except that the impact absorbing layer 1 and the impact absorbing layer 2 in Example 5 were produced using the impact absorbing layer-forming composition CU-3 shown below.

(Impact absorbing layer forming composition CU-3)
Septon 2063 (Kuraray Co., Ltd.) was added to a mixing tank containing MIBK (methyl isobutyl ketone) in advance, and stirred. The content of each component is as shown below. The obtained composition was filtered through a polypropylene filter with a pore size of 10 μm to obtain impact absorbing layer forming composition CU-3.

Septon 2063 25.0 parts by weight MIBK 75.0 parts by weight

(Example 7)
A front panel was prepared in the same manner as in Example 5, except that the composition for forming an abrasion-resistant layer HC-2 in Example 5 was replaced with the composition for forming an abrasion-resistant layer HC-3 shown below.

<Preparation of Composition for Forming Abrasion-Resistant Layer>
(Composition for forming abrasion-resistant layer HC-3)
A-TMMT (manufactured by Shin-Nakamura Kogyo Co., Ltd.), DPCA-30 (manufactured by Nippon Kayaku Co., Ltd.), Irgacure 127 (manufactured by BASF Corporation), compound 4 (conductive compound A), and a MIBK (methyl isobutyl ketone) solution containing 30% by mass of the polymerizable resin (1) described in JP-A-2015-168719 were charged into a mixing tank containing MIBK (methyl isobutyl ketone) in advance and stirred. The content of each component is as described below. The obtained composition was filtered through a polypropylene filter having a pore size of 0.45 μm to obtain a composition for forming an abrasion-resistant layer HC-3.

A-TMMT 26.2 parts by weight DPCA-30 7.1 parts by weight Irgacure 127 1.0 parts by weight Compound 4 (conductive compound A) 3.2 parts by weight MIBK solution of polymerizable compound (1) 1.2 parts by weight MIBK 50.4 parts by weight

(Storage Modulus)
The storage modulus measured at a temperature of 25° C. and a frequency of 1.0×10 ⁶ Hz is shown below.
・Clarity LA2140 Storage modulus 0.1 GPa
・SK-2057 Storage modulus 0.96 GPa
・Hybra 7311F Storage modulus 0.57 GPa
Septon 2063 Storage modulus 0.01 GPa

(evaluation)
A glass sheet for evaluation having a thickness of 0.4 mm was placed on the surface of the front panel produced in Examples 1 to 5 on the side having the impact absorbing layer 1 of the resin film 1, and a ball drop test was performed.

The ball drop test was performed by dropping an iron ball (diameter 32 mm, weight 130 g) from a height of 20 cm onto the front panel.

The comparative example was a case where no front panel was installed. In the comparative example, the evaluation glass broke, but when the front panels of Examples 1 to 5 above were installed, the evaluation glass did not break or the degree of breakage was suppressed compared to the comparative examples. Therefore, it was found to have excellent impact resistance.

Although the present invention has been described in conjunction with its embodiments, we do not intend to limit our invention to any of the details of the description unless otherwise specified, and believe that the appended claims should be interpreted broadly without departing from the spirit and scope of the invention as set forth in the appended claims.

Claims (2)

A front panel having, from the viewing side, a resin film, an impact absorbing layer, a resin film or ultra-thin glass, and an impact absorbing layer in that order, wherein the impact absorbing layer has a storage modulus E' of 2 GPa or less at a measurement temperature of 25°C and a frequency of 1.0 x 10 ⁶ Hz, and the ultra-thin glass has a thickness of 100 μm or less. A foldable device using the front panel described in claim 1.